Thanks @ericrosenbaum!

Fix issue with sound upload button not always working, and correctly cache sound type if given an mp3.

There's a subtle difference in behavior between mouseup and click. Using mouseup allows you to close the menu by clicking its opener item.

whoops

It's shifted downward to not overlap the menubar, since it's hard to make a child z-indexed below its parent.

It's a cleaner API IMO but ended up being a messy implementation...

These use a technique where the save/load functionality is passed from the component to its children via a function argument.  I opted for this rather than a higher order component because it is more readable and requires fewer intermediary components.

This could just as easily been done with a higher order component and would be happy to change it to that instead.

There is a performance implication since there is a function being defined in render. However the menu bar is not a highly re-rendered component, so I thought it would be ok in this case.